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Research of the month: vitamin D supplements don’t cut heart disease risk

Lucy Goodchild van Hilten, 22nd February 2019

In another of our monthly blog post written by Science Wordsmith Lucy Goodchild, we explore the findings and attention around a piece of research published in the previous month that caught the public’s attention. Listen to the accompanying podcast here.

Why the results of a trial in the New England Journal of Medicine hit the headlines

The world has been captivated by sunshine pills: vitamin D supplements hold so much promise, having been hailed as a miracle cure for a whole range of things, from bone strength to immune system function to cancer reduction. But do they really have such a positive impact on our health?

To address these knowledge gaps, researchers conducted a large-scale, randomized, double-blinded clinical trial looking at the effects of vitamin D, with and without omega-3 fatty acids, in nearly 26,000 men and women in the US. The results, published in theNew England Journal of Medicine, suggest that taking vitamin D supplements doesn’t reduce the risk of heart disease or cancer, but there is a signal that it might reduce the risk of cancer death.

Read the study: “Vitamin D Supplement and Prevention of Cancer and Cardiovascular Disease

“Many studies have looked at blood levels of vitamin D, and higher blood levels have been linked to lower risk of cancer, cardiovascular disease and many chronic diseases,” said Professor JoAnn Manson, lead author of the study and a Professor in the Department of Medicine at Harvard Medical School and the Department of Epidemiology at Harvard T. H. Chan School of Public Health in the US. “However, these are observational studies that are not testing a cause and effect relationship. As we say in epidemiology, correlation does not prove causation, and there are many potential confounding factors.”

Professor JoAnn Manson, Professor in the Department of Medicine at Harvard Medical School and Chief of Preventive Medicine at Brigham and Women’s Hospital in the US. Find out more about her work:

Spending time outdoors is one such factor: people who spend more time outdoors have higher blood levels of vitamin D. And people who spend time outdoors tend to be more physically active – walking or playing racquet sports, for example – and that kind of activity can also lower the risk of heart disease and cancer. So while certain health problems might be linked to low blood levels of vitamin D, that doesn’t prove that supplementing with vitamin D will lower the risk of those problems.

Some clear evidence was needed, and it came in the form of the Vitamin D and Omega-3 Trial, VITAL, which is the largest randomized clinical trial of vitamin D. The researchers looked at the health effects of taking two popular supplements – vitamin D and omega-3 – together and separately. Participants were split into four groups: the first received both supplements, the second received vitamin D and a placebo, the third received omega-3 and a placebo, and the last received two placebos.

The results of the five-year trial showed that taking vitamin D supplements did not significantly reduce the risk of heart disease or cancer. There was, however, an indication that taking vitamin D supplements could reduce the risk of death due to cancer – something that had been suggested in a previous meta-analysis.

“It’s possible that vitamin D affects tumor biology and makes tumors less invasive, less aggressive, less likely to metastasize, in which case, a reduction in cancer death would be plausible,” said Prof. Manson. “That was interesting, and we do want to continue to follow the participants for new diagnoses of cancer and cardiovascular disease, as well as for deaths and causes of death. We may have a clearer answer within another two years.”

Getting the story straight

Almost 40% of people in the US take vitamin D supplements in some form, making the results significant for a large proportion of the population, and therefore making the study very newsworthy. Prof. Manson and her colleagues expected there would be media coverage, so they took steps to ensure they got an accurate message out to people.

“Very often, patients start to call their doctors shortly after hearing about these studies,” she explained. “I think it’s critically important to have a simultaneous publication of the full article so that researchers and clinicians and even members of the public who want to learn more have a place to go to for additional details. They can read the report at length and see all the data, see the tables, see the figures and get the information that they need.”

On the day the two papers were published along with an editorial in the New England Journal of Medicine, Prof. Manson presented the results at the American Heart Association conference. It was a Saturday, but that didn’t slow down the media response. “It was extremely busy most of that day and the following several days, I did probably more than 100 interviews by the end of the whole process,” she recalled.

Discover the coverage:

The experience was mixed – some of the coverage was unbalanced and didn’t reflect the results accurately, making it frustrating at times. “I think it’s very challenging to cover a randomized trial like VITAL in a fully balanced way; the results were complex and nuanced,” said Prof. Manson. “What I think is very important is for the media is to put new research in the context of the totality of previous research. When a study is taken completely out of context and is just discussed in isolation, it’s much more likely that the results will be overstated in one direction or the other.”

There’s plenty more to understand about the VITAL results. Over the coming few months the team will publish more findings for other health outcomes, including diabetes, cognition, depression, autoimmune disorders and lung disorders. Prof. Manson and her colleagues will continue long-term follow-up with the cohort for at least two more years, including better understanding whether taking vitamin D supplements can reduce cancer deaths.

For now, the advice is that the trial doesn’t provide any clear reasons to start or stop taking vitamin D supplements. “Many people may want to just stay tuned for additional findings over the next six months or so and that may help them make decisions or talk with their healthcare providers,” said Prof. Manson.

“Although we didn’t find side effects or safety concerns with 2,000 IUs a day of vitamin D or with one gram a day of omega-3s, we do want to caution people against megadosing with these supplements – with much higher doses, there can be risks, including high blood and urine calcium levels, kidney stones, and bleeding. We also advise people to get omega-3s from their diet as much as possible, so by eating fish rather than taking supplements.”

Prof. Manson’s top tip for promoting research: “It’s important to think about which audience you’re trying to reach. Is it a message that’s ready for prime time in terms of the public? Or is it a message for other researchers? If there’s a message for the public, then I do think having a very responsible press release is helpful to increase the likelihood that the story will be covered in a balanced way. In this case, these are supplements that are already widely used, and it was important to get out the message that there weren’t tremendous benefits.”

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